(i) Technical Field
The present disclosure relates to an image forming apparatus.
(ii) Related Art
An image forming apparatus includes, for example, an image forming unit and a post-processing unit. The post-processing unit may be incorporated in the image forming unit. The image forming unit is an apparatus for forming an image on a sheet as a recording material. The post-processing unit is also called a finisher and applies a post-processing to a sheet or a bundle of sheets on which an image has been formed. Needleless binding (or needleless staple) and needle binding (or needle staple) are known as a post-processing. There are several methods for the needleless binding including a crimping method as a representative one. The crimping method is a method of pinching a bundle of sheets between upper and lower tooth rows to form a recessed or raised impression as a needleless binding part. In the needleless binding part, an entanglement of fibers occurs between sheets, which bind the sheets with each other.
JP-A-2013-170067 discloses a technique for dividing and binding a bundle of sheets to be bound with no needle by a predetermined unit or less when the bundle of sheets includes a large number of sheets.
JP-A-2015-001702 discloses a technique for selecting needle binding when the number of sheets to be subjected to needleless binding is equal to or larger than a predetermined number of sheets.
JP-A-2015-227038 discloses a technique for displaying information on sheets or a bundle of sheets that can be bound with no needle.
JP-A-2014-240126 discloses a technique for controlling a pressing force in accordance with the sheet moisture content in the crimping type needleless binding.
JP-A-2014-226799 discloses a technique for varying the pressing force holding time according to humidity in the crimping type needleless binding.
JP-A-2013-040024 discloses a technique for changing an operation speed according to, for example, humidity in needleless binding. However, the disclosed technique is a die cutting method and is not a crimping method that causes entanglement of fibers.
JP-A-2014-091249 discloses a technique for removing paper dust jammed between teeth in the crimping type needleless binding by blank beating. Further, JP-A-2014-091249 discloses a technique for controlling a pressing force according to the sheet moisture content in the crimping type needleless binding.
Needleless binding of a bundle of sheets forms a recessed or raised impression as a needleless binding part. The quality of the needleless binding part varies depending on the environment in which the bundle of sheets is placed. For example, in a low-humidity environment, there is a tendency that the holding force of the binding part (binding force between papers) decreases as compared to a high-humidity environment. There is a demand for preventing the quality of the needleless binding part from being contrary to the user's expectation.
In the crimping method, a recessed or raised impression is formed as a binding part on a bundle of sheets. When a defective point such as a rupture or a tear occurs in the binding part, the holding force of the binding part (binding force between papers) decreases. Therefore, it is required to prevent such defective part from occurring. In particular, there is a demand for preventing a defective point from occurring due to an excessive speed of binding operation under a specific environment. Meanwhile, it is also required to shorten the binding processing time as long as such a problem does not occur.
When a recessed or raised impression is formed as a binding part by pinching a bundle of sheets between a pair of tooth rows, paper dust may remain, depending on situations, in one or more spaces (i.e., valleys) between teeth and may gradually grow to a large size. When paper dust clogging which cannot be ignored occurs in any interdental space, a proper binding process cannot be performed. As a result, the holding force of the binding part (binding force between papers) is reduced. Or, such paper dust clogging may give an excessive load to a mechanism forming the binding part. Therefore, it is required to apply the operation conditions under which paper dust clogging hardly occurs. However, when such operation conditions are uniformly applied, depending on a situation, the operation conditions may be excessive countermeasures, which may cause another problem (e.g., deterioration of the quality of the binding part).